Conventional holographic recording media are formed by sandwiching a dried liquid holographic recording material, called as a photopolymer material, between a pair of transparent substrates.
A manufacturing method thereof includes: forming a frame on the top of a transparent substrate; injecting a photopolymer material into the frame (when any solvent is used, dry until most of the solvent in the material evaporates) for jellification; placing the transparent substrate on a lower press stage of a press machine with the material upward; pressing a second transparent substrate from the side of an upper press stage; and irradiating the outer periphery with ultraviolet rays in this pressed state, thereby curing the periphery of the holographic recording material before taken out.
During the foregoing pressing, the upper press stage and the lower press stage must be fine adjusted to a parallel space having a predetermined thickness (for example, 100 μm or so).
For this reason, conventional measures have been taken such that the transparent substrates are irradiated with light and the interference fringes of the reflected light are checked to increase the precision of the parallelism of the press stages for fabrication. Otherwise, spacers having the intended thickness of the holographic recording medium, including the transparent substrates, are used for pressing.
For the sake of increasing the precision of the parallelism of the press stages or using spacers having the same thickness as that of the holographic recording medium as described above, it takes time to fabricate the holographic recording medium. Improving the precision of the parallelism of the press stages also has limitations. Furthermore, when interference fringes are recorded onto the holographic recording medium, polymerization contraction can occur in the holographic recording material to cause deformation of the transparent substrates. In this case, if the contraction before and after holographic recording increases, there arises a problem because it becomes difficult to reproduce the recorded information accurately.